I am planning to tear down my old shrimp tank and set up a 50cm/45L tank for pygmy cories. I want to use sand, but also plant the background with the crypts from the shrimp tank. I was thinking of growth substrate under the sand but have some Tropica Soil Powder left from a previous setup, would it make sense to add that under plastic canvas or in bags and then sand on top? I want the tank to be as easy as possible, so not thinking of separate substrate areas. Or is say 2 cm of sand just as good for crypts? They now grow on rather thick layer of gravel with water column dosing.